ISSS-2005/SE-04 Mems Based Humidity Sensor

Humidity plays a very major role in various industries. Monitoring and controlling the humidity is of great importance for the reliable operation of various systems. Micro Electro Mechanical Systems {MEMS} owing to their high reliability and good scaling factors have replaced many conventional sensor systems. Micro Cantilever systems have been found to be highly suited for sensing purposes. A Micro Cantilever Humidity Sensor based on Capacitive principle is designed and various analyses were performed on the sensor. The polyimide being the sensing layer is coated on the Cantilever beam. The beam is provided with movable electrode. As humidity increases, the polyimide absorbs water vapour and causes increase in mass of the beam. The deflection of beam causes capacitance change, which is related to the change in humidity. The design also incorporates a Platinum based temperature sensor to measure the temperature and also a Platinum based heater to regenerate the sensing layer for obtaining next measurement. The structure was designed using Coventorware and Intellisuite. Many analyses were done and the structure was simulated for real environmental conditions, like pressure etc. The results were very close in both these design packages. The structure showed a good linearity and good sensitivity in the regions from 10 – 40 % RH in all temperatures in human adaptive ranges. The beam had an appreciable deflection causing a notable change in capacitance. The sensitivity was in order of Pico to Femto farads per %RH change